I don't know what kind of bacteria, I was only using gentian violet to stain them, and they were the typical bar shape.
I was using a microscope that was probably purchased for one of my "sciencey" things with my kids. Hence only having gentian violet to stain with. It was probably less than $20 when first purchased.
I have been checking it semi-regularly just to know when it started growing stuff, but I actually checked it today when I noticed cloudiness in one of my foamer bottles. I was wondering what was growing in there, and checked the tester as long as I had everything out. The foamer bottle happened to be the one that went to New Orleans and back with us, and was the last of a batch made back in January of 2016, so no telling what was going on. I just know that I did not mind sacrificing half an inch of diluted liquid soap.
I am probably not going to sell, and probably never going to use preservatives. I have recently given liquid soap away to "non-immediate" family and friends for the first time. I only did the first dilution, gave them directions to dilute for the foamer bottles, and made them sign a paper that said that they knew that there were no preservatives in there, and that it needed to be stored in the refrigerator to prevent spoiling. And that was before I found cloudiness and spoilage. I tend to store my paste in 1 lb packages, which gives me about a 4-6 month supply of liquid soap for my foamer bottles. That paste gets set into the bottom drawer of the fridge because I got tired of shuffling it around my pantry shelves. The diluted soap just gets stored under the kitchen sink.